In recent years, expectations for a PDP (plasma display panel) and a liquid crystal display device have been increased as a thin display device that replaces a CRT (cathode-ray tube). In particular, the liquid crystal display device is excellent in thinness and lightness, lower power consumption and the like, and is expected to be in increasing demand hereafter.
The display of the liquid crystal display device is performed by utilizing a light source referred to as a backlight device arranged on the back side of a liquid crystal panel. Liquid crystals in the liquid crystal display device themselves do not emit light, and the luminance of the liquid crystal display device largely depends on the amount of light emitted from the backlight device.
FIG. 14 is a block diagram showing an example of a conventional backlight device. The backlight device of FIG. 14 includes a plurality of drive circuits 50 and a plurality of fluorescent lamps 60, each drive circuit 50 being connected to two of the fluorescent lamps 60.
Each drive circuit 50 supplies a drive voltage to the fluorescent lamps 60 respectively connected thereto. By this, the respective fluorescent lamps 60 light up.
Here, in the backlight device of FIG. 14, the drive circuits 50 are controlled independently, and the drive voltages supplied from the respective drive circuits 50 to the corresponding fluorescent lamps 60 are asynchronous. Therefore, although the two fluorescent lamps 60 connected to the same drive circuit 50 light synchronously, the fluorescent lamps 60 connected to different drive circuits 50 light asynchronously.
In the liquid crystal display device using the above-described backlight device, when the number of the fluorescent lamps 60 increases, interference noise by the plurality of fluorescent lamps 60 is caused on the liquid crystal panel.
A method that solves the above-mentioned problem is disclosed in JP 3293592 B.
As shown in FIG. 15, a backlight display device according to JP 3293592 B includes a plurality of drive blocks 70 and a plurality of lamps 81 to 88, where two of the fluorescent lamps 81-88 are connected to each drive block 70. In the backlight display device of FIG. 15, the lamps are driven such that an oscillation waveform of the lamps 83, 84 is in opposite phase to an oscillation waveform of the lamps 81, 82, an oscillation waveform of the lamps 85, 86 is in opposite phase to the oscillation waveform of the lamps 83, 84, and an oscillation waveform of the lamps 87, 88 is in opposite phase to the oscillation waveform of the lamps 85, 86. By this, the interference noise by the plurality of lamps 81 to 88 can be cancelled.
However, in the above-described liquid crystal display device of JP 3293592 B, when operating a remote controlling equipment having a transmitter and a receiver that respectively transmits and receives an infrared signal of a high-frequency band (approximately 30 kHz to approximately 60 kHz) near the liquid crystal display device, malfunction occurs in the receiver of the remote controlling equipment. Here, the transmitter of the remote controlling equipment is, for example, a remote control for operating the liquid crystal display device, and the receiver is, for example, an infrared-ray receiving sensor IC (integrated circuit) installed in the main body of the liquid crystal display device.